Not able to get the v3.0.0 for TB115 CSS to work

[No-good-deed-goes-unpunished]

Hi,
The only thing that does work for me is removing the line from the tab. which is great.
I'm not sure how much tab customization is possible with this CSS, but I'd really like to keep the tabs as close to what they look like in Thunderbird 52, which I am hoping to upgrade from, to 115.

I've got the preferences set to allow legacy stylesheets.
I am old and cannot read dark mode screens at all, and there is a major shortage of decent themes with text that allows Thunderbird to work in light mode, so I am struggling to get TB to look at all appealing. Not sure how much of that is customizable with your script.

I'm looking for some guidance on how to make the CSS work. As I said, the only thing that works for me is the line on the tabs.

I'm using TB 115.4.1. I did a clean scratch install, but on my production machine I hope to upgrade from 52.9.1 --> 78.14 --> 115.4.1
Windows 10, 21H2 19044.3570.

Attached is what my tab bar looks like now

At the risk of being pedantic, there is a typo in the script on line 132. Should be "might Not

On v52 I have also added some code in userContent.CSS to make the highlight a rust color so that I could see when a folder has new messages as the default was impossible for me to see. This doesn't work in 115. Is it possible to set this with this script?